The ingestion rate of meiobenthos has been measured using a radioisotope as a tracer. However, this methods tended to overstimate, bacause of the direct use of the tracer by the organisms. In the present study, I firstly intended to develop a new method to measure the ingestion rate of meiobenthos using colloidal gold as a tracer. However, gold was found to be not suitable as a tracer because it is difficult to distinguish gold from zinc in the energy diffusive X-ray analysis (EDX). Use of iron instead of gold as a tracer, on the other hand, gave excellent reslts. It was especially advantageous to use colloidal iron than gold, because ingestion rates could be quantified accurately not by the time consuming method that the observation fo ultra-thin sectinis using transmission electron microscope, but rather easier way that using EDX equipped with the scanning electron microscope. Using this new method, ingestion rates of four species of shallow water nematodes in Otsuchi Bay could be measured accurately. With data on respiration rates and seasonal fluctuation of nematode aseemblages, the yearly production of nematode communtity also could be measured directly. In the beginning, I intended to use the new method to measure the ingestion rates of deep-sea meiobenthos. However, dut to the delay in developing the new method, I missed the chance to apply the new method of using colloidal iron to the deep-sea species, but I simply used colloidal gold as a during the Hakuho Maru cruise to the Antarctic Ocean. The radiation analysis is the most sensitive to measure the gold quantitatively. I woul like to apply the method to the materials I obtained during the cruise. In addition, I would like to fed iron labeled POC to the deep-sea animals in situ using manned submersible.